Navigation device and method for determining orientation of vehicle

Abstract

A vehicle includes an acceleration sensor that generates an output of an acceleration in a direction of the acceleration sensor. The output of the acceleration includes information on an orientation of the acceleration sensor relative to the vehicle. A method for determining an orientation of the vehicle includes (i) detecting a first output of the acceleration sensor; (ii) memorizing the first output as a reference orientation value, (iii) correcting the memorized reference orientation value, based on an average of outputs generated by the acceleration sensor while the vehicle travels after the first output is generated; and (iv) determining an orientation of the vehicle when the vehicle travels, based on the corrected reference orientation value and a second output of the acceleration sensor.

1. A navigation device in a vehicle including a distance sensor for detecting a travel distance of the vehicle, the navigation device comprising:
 an acceleration sensor that generates outputs of accelerations in a front-rear, a lateral, and a vertical directions of the acceleration sensor; and 
 a correction unit that
 detects a first group of outputs of the acceleration sensor with respect to the three directions, the first group including information on an orientation of the acceleration sensor relative to the vehicle, 
 memorizes the first group as reference orientation values, 
 corrects the memorized reference orientation values with respect to the three directions, based on three averages of outputs generated by the acceleration sensor while the vehicle travels after the first group are generated, each average being an average of outputs with respect to each of the three directions, 
 determines an orientation of the vehicle when the vehicle travels, based on (i) the corrected reference orientation values and (ii) a second group of outputs of the acceleration sensor with respect to the three directions, and 
 corrects a travel distance detected by the distance sensor, based on the determined orientation of the vehicle. 
 
 
   
   
     2. The navigation device of  claim 1 , wherein
 the acceleration sensor is fixed in a casing of the navigation device, 
 the orientation of the acceleration sensor is detected as an orientation of the casing. 
 
   
   
     3. The navigation device of  claim 2 , further comprising:
 a gyro sensor fixed in the casing and used to detect an orientation of the vehicle. 
 
   
   
     4. The navigation device of  claim 3 , further comprising:
 a position calculation unit that calculates a position of the vehicle based on outputs of the acceleration sensor, the distance sensor, and the gyro sensor. 
 
   
   
     5. The navigation device of  claim 1 , wherein
 the correction unit memorizes the detected first group when the vehicle is stopping after the navigation device is supplied with electric power for a first time since the navigation device is provided in the vehicle. 
 
   
   
     6. The navigation device of  claim 1 , further comprising
 an operation unit that inputs an instruction by a user who has determined that the vehicle is in a horizontal orientation, wherein 
 the correction unit memorizes the detected first group when the instruction is inputted by the operation unit. 
 
   
   
     7. The navigation device of  claim 1 , wherein
 the correction unit corrects the memorized reference orientation values by calculating three weighted averages, each of which is, with respect to each of the three directions, a weighted average of both the reference orientation value and the average of outputs. 
 
   
   
     8. The navigation device of  claim 1 , wherein
 the correction unit
 calculates a given acceleration caused by a change in a speed of the vehicle, based on a travel time and a travel distance obtained based on the distance sensor, and 
 calculates an average of differences as a first average with respect to the front-rear direction of the three averages, each of the differences being obtained by subtracting the calculated given acceleration from an output of the acceleration sensor in the front-rear direction. 
 
 
   
   
     9. The navigation device of  claim 1 , wherein
 the outputs of the acceleration sensor used for calculating each of the three averages are within a predetermined range including the corresponding reference orientation value of the three reference orientation values. 
 
   
   
     10. The navigation device of  claim 1 , wherein
 the correction unit memorizes the detected first group when one of a first and a second conditions is satisfied, 
 the first condition is satisfied when the vehicle is stopping after the navigation device is supplied with electric power for a first time since the navigation device is provided in the vehicle, 
 the second condition is satisfied when an operation unit inputs an instruction by a user who has determined that the vehicle is in a horizontal orientation, 
 the correction unit corrects the memorized reference orientation values by calculating three weighted averages, each of which is, with respect to each of the three directions, a weighted average of both the reference orientation value and the average of outputs by using one of a first and a second coefficients for weighting the average of outputs, and 
 the second coefficient corresponding to the second condition is smaller than the first coefficient corresponding to the first condition. 
 
   
   
     11. The navigation device of  claim 3 , wherein
 the correction unit
 detects the orientation of the casing, and 
 corrects, based on the detected orientation of the casing, a heading direction of the vehicle obtained based on an output of the gyro sensor. 
 
 
   
   
     12. The navigation device according to  claim 4 , further comprising:
 a displaying unit for displaying a map image; and 
 a map image drawing unit for causing the displaying unit to display a current position mark and a map image including a current position of the vehicle calculated by the position calculation unit. 
 
   
   
     13. A navigation device in a vehicle including a distance sensor for detecting a travel distance of the vehicle,
 the navigation device comprising: 
   
 an acceleration sensor that generates an output of an acceleration in a front-rear direction of the acceleration sensor, the output including information on an orientation of the acceleration sensor relative to the vehicle; and 
 a correction unit that
 detects a first output of the acceleration sensor, 
 memorizes the first output as a reference orientation value, 
 corrects the memorized reference orientation value, based on an average of outputs generated by the acceleration sensor while the vehicle travels after the first output is generated, 
 determines an orientation of the vehicle when the vehicle travels, based on (i) the corrected reference orientation value and (ii) a second output of the acceleration sensor, and 
 corrects a travel distance detected by the distance sensor, based on the determined orientation of the vehicle. 
 
 
   
   
     14. A method for determining an orientation of a vehicle including an acceleration sensor that generates an output of an acceleration in a direction of the acceleration sensor, the output including information on an orientation of the acceleration sensor relative to the vehicle,
 the method comprising:
 detecting a first output of the acceleration sensor; 
 memorizing the first output as a reference orientation value, 
 correcting the memorized reference orientation value, based on an average of outputs generated by the acceleration sensor while the vehicle travels after the first output is generated; and 
 determining an orientation of the vehicle when the vehicle travels, based on (i) the corrected reference orientation value and (ii) a second output of the acceleration sensor.